The club said he has a "Grade 2" strain on a scale of 1 to 3. Zambrano suffered the injury beating out a bunt for a base hit to lead off the Cubs' four-run fifth inning in Sunday's 6-4 victory over Florida.
"We did the right thing," said manager Lou Piniella. "The danger with this thing is, too early (coming back), you really hurt it more, and now it's a 6-to-8 week thing, and that we can't have."
The Cubs say Zambrano's injury will take the full DL time -- and possibly up to 2 1/2 weeks -- to heal. He'll be eligible to return May 19 when the Cubs open a series in St. Louis. Piniella said Zambrano won't necessarily start that game, but that he should be able to do so sometime that week.
Neither Zambrano nor the Cubs expressed any misgivings about Zambrano bunting to lead off an inning. Piniella has used Zambrano three times as a pinch hitter this year.
"If my legs feel 100 percent, I'll be the same," Zambrano said of his approach to the game. "I have to work on my game, and I have to hustle."
The Cubs will call up Randy Wells to start Friday's game at Milwaukee. That's Zambrano's slot in the rotation.
CUBS 4, GIANTS 2
Ryan Theriot hit his third homer of the season, a two-run drive to left field in the second inning, to put the Cubs ahead 3-0. RHP Ryan Dempster cruised for seven innings, giving up five hits and two runs. Kevin Gregg earned his fourth save. The Cubs have won four in a row.
NOTES, PLAYER NEWS
--Wells will fill Zambrano's spot in the rotation. Wells tuned up with three scoreless innings Monday for Iowa, lowering his ERA to 2.77 to go with a 3-0 record. The Cubs are carrying 11 pitchers, down from 12, but general manager Jim Hendry says the Cubs will get back to 12 and stay at that number for most of the season. Wells, a 2002 draft pick of the Cubs, pitched briefly in the majors last year with Toronto and the Cubs.
--Dempster rebounded from a 10-0 loss last week at Arizona. After last Friday's game at Wrigley, he went to the bullpen and worked with pitching coach Larry Rothschild.
"Early on in the season when I'd get runners on base, I wasn't mentally sticking with pitches," said Dempster, who added he worked on keeping the ball down.
--Theriot's homer was his third of the season and third in four days. The three homers match Theriot's career high, set in 2006 and 2007. He homered once last year. The recent power surge has come as Piniella has instructed Theriot to "drive" the ball with men on base instead of "aiming" it.
--IF Bobby Scales was selected from the roster of Class AAA Iowa to immediately fill the roster spot left open whenZambrano was placed on the disabled list with a strained left hamstring. Scales, 31, is a career minor-leaguer who has never appeared in a big-league game. He went to spring training with the Cubs as a non-roster player in 2008 and this year.
--RHP Carlos Marmol worked his fifth game in six days. He pitched one scoreless inning, giving up a hit while striking out two. Marmol is likely to get Tuesday off, along with a few regulars.
--The Sports XChange
NASHVILLE 5, IOWA 1 (CLASS AAA)
At Des Moines, the Cubs (13-10) were held to five hits in their fourth straight loss Monday. RF Brad Snyder (2-for-4) paced the Cubs’ offense with two hits, including a triple and his sixth home run. Snyder has hit safely in 14 consecutive games dating back to April 17 and is batting a season-high .308 through 21 games. LHP J.R. Mathes (3-3) suffered the loss in relief, allowing two runs and three hits in one inning of work. RHP Randy Wells started and pitched three scoreless innings, allowing no hits and one walk. He struck out two batters and was on a pitch count of 40.
TENNESSEE 3, HUNTSVILLE 2 (CLASS AA)
At Huntsville, Ala., LF Ty Wright (2-for-4) paced the Smokies’ (12-9) offense with two hits, including two doubles and an RBI in the victory Monday. Tennessee collected six hits total with 1B Blake Lalli (1-for-2, walk) hitting his fourth home run and 2B Tony Thomas (1-for-4) hitting his fifth home run. LHP James Russell (2-2) got the win in relief with two scoreless innings. He allowed two hits. RHP Marcos Mateo started and tossed four innings, allowing one earned run on four hits. He walked three batters and struck out one.
DAYTONA 6, TAMPA 0 (CLASS HIGH-A)
At Tampa, Fla., LF Tyler Colvin (4-for-5) collected a season-high four hits in the Cubs’ (11-13) victory Monday. He doubled twice, scored two runs and drove in a run. DH Russ Canzler (2-for-4) added a double and a three-run home run, his second of the season en route to a four-RBI night. The Cubs’ first four batters combined for 10 hits. Three Daytona pitchers combined on a seven-hitter with RHP Rafael Dolis (1-3) picking up his first win by tossing five shutout innings. He allowed two hits and three walks to go with four strikeouts. LHP Dustin Sasser and RHP Henry Williamson each tossed two scoreless innings.
PEORIA 4, CEDAR RAPIDS 3 (CLASS-A)
At Cedar Rapids, Iowa, the Chiefs (12-11) tallied 12 hits in the victory Monday. 2B Junior Lake (3-for-4, RBI) led the offense with three hits, and RF Nelson Perez (2-for-4, home run), 1B Rebel Ridling (2-for-5, double) and LF Kyler Burke (2-for-5, RBI double) each added two hits. RHP Chris Archer started and went two innings, allowing one unearned run and one hit. RHP Josh Whitlock (1-1) got the win in relief, tossing two innings and allowing two runs on three hits. He struck out two batters.
InsideTheIvy.com correspondent Kelsey Knutson in Des Moines contributed to this report.